NYC-WTC_000232959

NYC 9/11 Public Portal Document

Frequency Distribution of Weight Change in Seiected Bianks

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16

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12 PMIOO PMIO o 10 0) PM4

I 3 PM2.5

-I- Lower LOD Upper LOD 6

: I 2 - ------------ ^:5—5—

0+- 4 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 Weight Change [mg]

The dashed vertical lines show the upper and lower limits of detection expected for this method (-1-/- 0.03 mg). The distance between limits of detection represents the maximum weight gain expected for the blanks if the entire sampling procedure was followed as required by standard sampling methodologies. All of the size fractions had at least two blanks outside the limit of detection boundaries. (The two out of range blanks for PM 100 are not shown on the graph because they are also beyond the boundaries of the graph). Approximately 6% of the PMIOO, 70% of the PMIO, 57% of the PM4, and 8% of the PM2.5 blanks had weight changes greater than the limit of detection.

In general, blanks are used (1) to assess the ability of the sampling and laboratory analysis methodology to accurately estimate the concentration of particulate matter in the air at the sampled location and (2) to validate that there is no filter contamination problem from the time the blanks are initially weighed in the laboratory until the time the blanks are weighed in the laboratory after sampling. Errors could occur at any step in the process.

The large weight change of the blanks indicates errors in either the laboratory weighing process or the air sampling process. The graph illustrates that the results of the airborne particulate matter sampling cannot be used to reliably estimate the actual concentration of any of the particulate matter size fractions; therefore, the entire data set was rejected from further consideration.

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